I bought a 92 coupe last fall and have just recently been experiencing erratic performance. After all the horror stories I've read about the optispark, I'm suspecting it may be the source of my woes, but would like to solicit outside opinions. Initially, I noticed this problem under light acceleration while in overdrive at lower speeds (under 45 mph). Unless I either downshifted to drive, or gave it a healthy dose of throttle, the engine would miss slightly. This went on for a couple weeks and was more of an annoyance than a problem. Late last week, however, under hard acceleration from a standstill, the engine began to intermittently miss and backfire. I thought it might be from bad gas, water in the gas, etc (I live in north Florida and it has been COLD...ie under 30 degrees lately :-). This situation remains intermittent but typically only occurs when accelerating from lower rpms. Since I bought the car from a dealer, I don't know the intimate details of it's maintenance history. The plug wires look new (AC Delco), and I pulled the two easiest plugs to get to and they looked reasonably new, but the optispark is of unknown age. I welcome any suggestions, ideas, and helpful hints anyone may have.

Thanks in advance,
Rick

 

Have you tried to pull any codes? It may be the opti but don't be in a big hurry to condem it. Misses upon hard acceleration can be a lot of things ie: coil, plugs .....check for codes first.

 

How many miles on your '92. I have read that the life expectancy of the Optipuks is anywhere from 60K miles to 90K miles.

But take 'ittlfly' advice and pull the codes before you do anything. Could just as easily be fuel pump, or filter, or regulator, or injectors, etc. Pulling the codes is the best place to start your diagnostic journey in your quest for a smooth running Vette!!

 

Thanks to both of you for your quick replies. I forgot to mention, my car has 93k+ miles on it now...it had 88k and change when I bought it and thought I had been graced with a trouble-free example up until now. As for pulling the codes, I bought the Helm's manual a couple months ago, but I haven't had a chance to try reading the codes yet. I need to get busy with actually READING the book to find out about the methods and equipment necessary for pulling the codes to help identify the culprit. In the mean time, I'm just annoyed and sad that I have to rely on my old truck for a reliable daily driver!

Rick

 

To pull error codes from your ECM/PCM, all you need to do is short pin A and pin B on your ALDL(12 pin connector under your right knee when sitting in driver seat).
You can use a thin wire or paper clip to short these pins, general procedure:
1- keys out of ignition
2- short the 2 pins mentioned (be careful, don't need to force hard into ALDL)
3- turn on ignition, but do not start engine
4- look at your SES light, it should start blinking, error codes must be desiphered like morris code
5- first code will be a set of three 12's ...this is not error code, only idicates start of reading
6- error codes will come after first three 12's, and they will end at next set of three 12's
7- If there are no error codes, you will only see a series of 12's
8- When finished, turn off ignition, remove shorting wire or paper clip.

Here are a couple of URL's describing the ALDL numbering scheme(your '92 has a OBDI style 12 pin connector, unlike newer OBDII 16 pin connectors)

use this site to understand your ALDL pin numbering scheme for OBDI type connector, and a better description of how to decode the 'blinking' SES light(remeber, only need to short pin A and pin B to read Diag codes)
http://www.obd1.com/

use this site to determine what the diagnostic codes mean for your engine type:
http://www.troublecodes.net/GM/

Your ALDL connector should look like this:



Good luck...and keep us posted...

 

Thanks for the details on checking the codes. Using a paperclip for a jumper, the only thing I received was a steady stream of 12's. So, I guess I should be happy that it's not a 16, huh? :-) Still, I don't know why I get the hesitation as described before, particularly around 2000 rpm. I ran a bottle of Iso-Heet water remover through the last 3/8 tank along with a bottle of injector cleaner. Not surprisingly, this didn't make much, if any, difference. Now I'm left to wonder about the other 6 plugs that I didn't already check (they look like a real joy to change!), maybe the knock sensors, fuel filter, etc, etc... Any other ideas will be appreciated.

 

Since you do not have any history on maintanance, I would do the following:
- Get flashlight and do a visual on the parts of the Opti that you can see below the TB. See if it has a lot of "gunk" build up. If it doe's, I think you need to assume it is the original Optispark. That means you have 94K miles on this Opti, and it MIGHT be the source of your hesitation/backfiring problems.

- Again, before condeming the Opti, check your fuel delivery system. Check your fuel pressure at idle, check FP blead down(leaking injectors if pressure drops fairly rapidly AFTER engine turned off). I believe that it is normal for the pressure to bleed down to 0psi after 24 hours of downtime, but you should not be able to notice any bleed down in 5 or 10minutes after shutting engine off. Also could be a an injector(s) which is not atomizing the gas good enough. One always hopes that the injector cleaner would cure this type of ailment, but not always the case.

- Check for shorts from spark plug wires, coil wire, etc. If any of these wires are shorting, the effects may be more pronounced at higher RPM's. The highr the RPM's, the higher the voltage, therefore easier for electricity to jump from insolation to Ground. Do a visual in a dark place with engine on, and see if there are any "lightning bolts" arcing near plug and coil wires. The problem with this is that you may not be able to see so well due to hidden routing.

You may want to start another thread on the behavior of failing OptiSparks. See if your symtoms are inline with an Opti going bad. I have read many posts that describe a MUCH better running engine after Optispark replacement. (Remeber: Water Pump replacement usually performed in addition to Opti replacement)

 

First of all, I want to thank MikeC4 for the ideas and suggestions. Further inspection revealed that ONLY the passenger side plug wires appear to be new AC Delco wires. The driver side wires look older, as does the coil wire. The third plug wire from the bottom of the opti on the passenger side wasn't seated all the way either (heard the second click when I pushed on it). The passenger side wires on the opti did have a fair amount of oily crud on them, but the front portion of the opti (brownish) was clean. Still have to suspect that the opti is the original, I can't imagine anyone going through the trouble of changing it and then only changing half of the plug wires.

I don't have anything to check the fuel pressure at the moment. After letting it sit overnight, there was no pressure at the schraeder valve on the fuel rail. I changed the fuel filter yesterday (what a royal pain that was) and took it out today to run it a bit. The low speed stumble is still very noticable when turning around 1200 rpms in OD and trying to accelerate mildly. If I downshift to drive before giving it gas, the stumble isn't as noticable, but it still doesn't feel quite right. Given the looks of the plug wires on the drivers side, I need to spend an afternoon (or two??) replacing ALL the plugs and wires and see how it turns out.